[WIP] Async Signals #3344

Job	Run time
doc-lints	41s
godot-itest (macos)	1m 8s
license-guard	30s
clippy	1m 40s
godot-itest (windows)	3m 4s
run-examples	1m 23s
godot-itest (linux-full)	2m 22s
unit-test	2m 29s
godot-itest (linux-features-experimental)	2m 10s
rustfmt	12s
godot-itest (linux-4.1)	1m 10s
godot-itest (linux-4.2)	55s
godot-itest (linux-4.3)	1m 1s
godot-itest (linux-memcheck)	2m 18s
ci-status	1s
	21m 4s

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